Meniscus formation during tracheal instillation of surfactant

Abstract

The method of surfactant instillation into the lungs for treatment of neonatal respiratory distress syndrome is an important attribute of delivery, and it may determine the overall efficacy of treatment. Previous studies primarily focused on the rate at which the bolus is instilled. These findings show that rapid injections lead to a more homogenous distribution, whereas slow infusions drain into the dependent lung with respect to gravity, resulting in a heterogeneous deposition. These results suggest that it is beneficial to form a meniscus, from which a more homogenous dispersal can proceed. The objective of the present study was to develop a functional criterion for meniscus formation during bolus injection. An in vitro experiment was used to examine the clinical setting of surfactant instillation. The physical variables examined were the bolus viscosity (mu) and density (rho), gravity (g), injection rate (Q), orientation of the trachea with respect to gravity (theta), tracheal size (D), surface tension (gamma), and catheter size (d). All quantities were varied, except gravity and catheter size. Experimental results show that a meniscus will form when NSt > 0. 004Re2/3, where NSt is Stokes number and Re is Reynolds number, NSt = muQ/D4rhogsintheta, a ratio of viscous effects to gravitational effects, and Re = rhoQD/d2mu, a ratio of inertial effects to viscous effects. Rapid injections, high viscosity, and small inclination with respect to gravity promote meniscus formation. These results can be used to refine the guidelines for administration of surfactant replacement therapy.

Pulmonary Distribution of Lucinactant and Poractant Alfa and Their Peridosing Hemodynamic Effects in a Preterm Lamb Model of Respiratory Distress Syndrome

“…The results of this study are in accordance with reports that uniformity of surfactant distribution improves as volume of surfactant administered is increased (3). Optimal distribution can be achieved if a rapidly injected bolus accumulates in the airway to form an occluding column of liquid that is advanced into more distal airways by positive airway pressure (15). At airway branches, the surfactant column is then distributed more evenly between branches, resulting in relatively even distribution relative to alveolar volume.…”

Draining Collars and Lenses in Liquid-Lined Vertical Tubes

“…Of the twenty-odd generations of bifurcating airways in the human adult lung, those beyond about the tenth generation have radii smaller than the capillary lengthscale (σ/ρg) 1/2 ≈ 1 mm (taking σ ≈ 10 g/s 2 ). Taking ≈ 0.1 in every airway, B is roughly unity at generation 15 (where the airway radius is about 0.3 mm (34) (35)(36)(37)) will shrink if they drain under gravity alone, and either rupture or form lamellae. Pressure gradients across such lenses and lamellae will undoubtedly be significant here too (28,35).…”

“…Taking ≈ 0.1 in every airway, B is roughly unity at generation 15 (where the airway radius is about 0.3 mm (34) (35)(36)(37)) will shrink if they drain under gravity alone, and either rupture or form lamellae. Pressure gradients across such lenses and lamellae will undoubtedly be significant here too (28,35). In these and in smaller vertical airways, for which B > B 1 , gravity will prevent collars created by capillary instability from growing to form lenses.…”

Three-dimensional model of surfactant replacement therapy

“…In SRT, the instilled mixture can form a liquid plug in the trachea (19), which then propagates through the tracheobronchial tree by forced inspiratory airflow. As the liquid plug propagates distally, it coats the airway walls, losing some of its mass, and also splits at bifurcations.…”